1. Field of the Invention
The invention relates to an applicator for applying a coating of an oxidizable photographic processing composition to a surface of a length of sheet material so as to initiate the formation of a visible image therein or in a length of exposed film which is to be subsequently superposed therewith.
2. Description of the Prior Art
The present invention relates to an applicator for applying a coating of a photographic processing composition, preferably in the form of a viscous liquid, to a length of sheet material prior to superposing it with a length of exposed film so as to initiate the transformation of a latent photographic image into a visible image. Alternatively, the sheet material may contain the latent photographic image and the visible image may be formed in the same sheet material or in a subsequently superposed sheet material. Examples of such applicators may be found in U.S. Pat. Nos. 4,307,955; 3,453,138; 3,307,468; and 2,435,719. In the U.S. Pat. No. 4,307,955 the applicator is adapted to apply a coating of a photographic processing composition to a length of sheet material prior to superposing it with a length of photographically exposed film so as to initiate the formation of a visible image in the film. The applicators described in the U.S. Pat. Nos. 3,453,138 and 3,307,468 apply such a coating to an exposed length of sheet material (film) so as to develop the latent images contained therein. The applicator described in the U.S. Pat. No. 2,435,719 patent includes a plunger-cylinder combination for dispensing drops of a viscous processing liquid between lengths of positive and negative materials prior to their introduction between a pair of spread rollers.
Generally, the photographic processing compositions used in applicators of the type described take the form of a liquid which is alkaline and as such is subject to aerial oxidation. Accordingly, measures must be taken to protect the processing liquid from evaporation as well as the oxygen in the surrounding atmosphere when the applicator is adapted for intermittent operation, vis-a-vis, the one time operation of the applicator in the U.S. Pat. No. 4,307,955. The applicator of the U.S. Pat. No. 2,435,719 provides some protection against the adverse affects of the atmosphere but, because of the design of it plunger, also provides a system in which substantially all of the processing liquid located in its cylinder may not be expressed therefrom during each operation of the plunger. Thus, the processing liquid which remains in the cylinder at the end of each stroke of the plunger (due to the segmented end of the plunger) is subjected to the contaminating affects of the atmosphere until the applicator's outlet is sealed. This processing liquid is then mixed with a new supply of processing liquid during each of the following operating cycles thereby possibly decreasing its ability to contribute to the proper formation of a visible image in a subsequently impregnated sheet material. The applicator of U.S. Pat. No. 3,453,138 has a liquid reservoir which relies upon a transfer roller and a pair of resilient doctor blades for maintaining its air tightness and for preventing the escape of the processing liquid. However, since it appears that a portion of the aforementioned transfer roller will always contain some liquid on its surface at the end of each coating operation, it would appear that this portion would become contaminated by the atmosphere and such contamination would be at least partially transferred to the liquid in the reservoir during subsequent coating cycles. Finally, the applicator described in the U.S. Pat. No. 3,307,468 provides an arrangement wherein an applicator roller is initially submerged within a processing liquid contained within a reservoir. The reservoir has a cover mounted for movement from an open position to a closed position wherein it provides some protection for the processing liquid against the adverse affects of the atmosphere. During a coating operation, the cover is opened and the applicator roller is partially raised from the processing liquid and rotated about its axis in contact with a length of sheet material so as to apply a coating of the processing liquid thereto. But, at the end of the coating operation, the applicator roller is returned to its original submerged position within the reservoir without its surface being cleaned, thus possibly contaminating the processing liquid.